1. Field of the Invention
The present invention relates to an electric vehicle, in which motive power from an internal combustion engine is supplemented by electric traction, and a fault detection method for an exhaust gas recirculation system of the internal combustion engine used for the electric vehicle.
2. Description of the Related Art
In vehicles which use an internal combustion engine such as a gasoline engine as a source of motive power, an exhaust gas recirculation (EGR) system, in which some of the engine exhaust gas is recirculated to an intake system to lower the maximum temperature of combustion and reduce the production of NOX, is known as a device for reducing NOX in engine exhaust. If a desired amount of exhaust gas recirculation is not obtained because of a fault in the engine gas recirculation system, the amount of exhaust NOX may increase. On the other hand, if the amount of exhaust gas recirculation excessively exceeds a desired amount, motive power deteriorates because of a significant deterioration in combustion, and the amount of exhaust products such as HC, CO, and black smoke, may greatly increase. Therefore, an EGR system equipped with a fault detection device capable of detecting whether or not exhaust gas recirculation is being performed properly is known.
In such a fault detection device, by opening and closing an EGR valve while the internal combustion engine is running, the change in negative pressure in the intake manifold is measured before and after opening and closing. If the value thereof is in a predetermined range, exhaust gas recirculation is determined to be normal, and if the value thereof is not in a predetermined range, exhaust gas recirculation is determined to be abnormal.
When the EGR valve is opened and closed during normal operation, torque shock occurs because of combustion fluctuation and thus motive power deteriorates. Therefore, a technique is known in which fault detection is performed while fuel supply is cut during deceleration and thus toque shock or the like is suppressed as compared to a case where fault detection of an exhaust gas recirculation system is performed during normal operation (for example, Jpn. Pat. Appln. KOKAI Publication No. 9-144609).
In recent years, an electric vehicle in which an internal combustion engine and an electric motor are used in conjunction as a source of motive power, that is, a hybrid vehicle has been put into practical use. During deceleration, such an electric vehicle may be propelled only by the power of the electric motor, by cutting the fuel supply to the internal combustion engine and eventually stopping the internal combustion engine. Therefore, if fault detection is attempted while fuel supply is cut during deceleration, the rotation of the internal combustion engine is stopped before completing the fault detection. As a result, there may be a case where a sufficient opportunity to perform fault detection of an exhaust gas recirculation system is not secured.
In order to solve the above-described problems, a technique is known in which, when fault detection starts while the fuel supply to an internal combustion engine is cut during deceleration, even though the cutting of fuel supply is finished and conditions for stopping the rotation of the internal combustion engine are satisfied, the turning over (constrained rotation) of the internal combustion engine is performed by an electric motor until a predetermined fault detection is completed, to generate a negative pressure in an intake manifold and thereby to continue the fault detection (for example, Jpn. Pat. No. 4274266). Accordingly, a sufficient opportunity to perform fault detection of an exhaust gas recirculation system can be secured.